Ink compositions for ink jet printing

ABSTRACT

An ink for ink jet printing comprising a pigment, a component selected from the group consisting of saccharides, derivatives thereof and polyols having 5 or more hydroxyl groups, and a resin emulsion. This pigment-type ink is excellent in preservability, does not cause obstruction in a nozzle, and can evenly produce an image.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pigment-dispersed aqueous inkcomposition suitable for an ink jet printing system.

2. Related Art

Dye-type ink compositions basically consisting of a dye and an aqueousmedium have been known as inks for ink jet printing. It has been pointedout that images produced by the inks of this type are poor in both lightresistance and water resistance because of the inherent properties ofthe dye. In order to solve this problem, inks prepared by using, insteadof a dye, a pigment have been proposed.

In the meantime, inks for ink jet printing are required to have thefollowing properties: to undergo no change in the physical propertiesduring long-term preservation; not to cause obstruction in a finenozzle; to produce sharp images with a high density; and to produceimages having high preservability (water resistance, light resistance,etc.). In particular, pigment-type inks are required to have highpreservability, i.e., the ability to stably maintain the pigment in adispersed state for a prolonged period of time, and not to causeobstruction in a nozzle while printing is conducted or when the printeris restarted after interruption of printing.

The following have been proposed as pigment-type inks:

Japanese Patent Publication No. 1426/1987 discloses an ink which isprepared by dispersing a pigment and a resin emulsion in water.According to this, the preservability of a pigment-type ink can beimproved by adding thereto an emulsion of a water-insoluble syntheticresin. However, the resin contained in the ink tends to solidify at anozzle tip to cause obstruction.

Japanese Laid-Open Patent Publication No. 157668/1980 discloses thatwhen a pigment is dispersed in a water-insoluble resin emulsion, thedispersion can be stably maintained even when the viscosity of thedispersion is relatively low. Furthermore, Japanese Laid-Open PatentPublication No. 217088/1989 discloses that the preservability and thefluidity of an ink can be improved by using an emulsion having aspecific film-forming temperature. However, even such inks are stillinsufficient in the stability at low- and high-temperature regions andcause obstruction in a nozzle.

Inks prepared by using a resin emulsion like the above are disclosedalso in Japanese Laid-Open Patent Publications Nos. 160068/1991 and18462/1992. There is however room for further improvement in thestability of these inks.

Japanese Laid-Open Patent publication No. 18427/1990 describes thatinositol is added to an ink so that the ink will not cause obstructionin a nozzle. However, since inositol has hygroscopicity, this ink ispoor in moisture-abrasion resistance (that is, when the surface of animage produced by this ink is touched by a hand or a finger, the imageis abrased, or the hand or the finger is stained with the ink).

It is also pointed out that a pigment-type ink for ink jet printing hasthe problem of unevenness of printing, which has not been cased by adye-type ink. Such an unevenness is remarkably found in a solid filledarea, like a diagram or a bar graph. To solve the problem of unevennessof printing is an important subject in the art.

We have tried to improved the unevenness of printing by increasing theconcentration of pigment in an ink and discharging the ink in excess,but failed. Thus, it seems that the unevenness of printing depends oncomposition of an ink composition.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a pigment-type inkcomposition for ink jet printing, which is capable of evenly producingan image, excellent in preservability and does not cause obstruction ina nozzle.

Another object of the present invention is to provide a pigment-type inkcomposition for ink jet printing, capable of producing an image whichhas a high optical density and is excellent in rapid drying propertiesand moisture-abrasion resistance.

We have now surprisingly found that the above object can be attained byadding saccharide or a certain polyol and a resin emulsion to an inkcomposition.

The ink composition for ink jet printing according to the presentinvention therefore comprises:

(a) a pigment,

(b) a component selected from the group consisting of saccharides,derivatives thereof and polyols having 5 or more hydroxyl groups, and

(c) a resin emulsion.

DETAILED DESCRIPTION OF THE INVENTION Component (a)

Any inorganic or organic pigment can be used, without particularlimitation, in the present invention.

Inorganic pigments include for example titanium oxide, iron oxide andcarbon black which is produced by a known method such as a contactmethod, a furnace method or a thermal method. Furthermore, organicpigments include for example azo pigments such as azo lake,water-insoluble azo pigments, condensed azo pigments and chelate azopigments; polycyclic pigments such as phthalocyanine pigments, perylenepigments, perinone pigments, anthraquinone pigments, quinacrideonepigments, dioxazine pigments, thioindigo pigments, isoindolinonepigments and quinophethalone pigments; dye chelates such as basicdye-type chelates and acidic dye-type chelates; nitro pigments; nitrosopigments and aniline black.

According to the preferred embodiment of the present invention, pigmentswhich have a high affinity for water are preferably used.

The particle diameter of the pigment is preferably 10 μm or less, morepreferably 0.1 μm or less.

According to the preferred embodiment of the present invention, thecomponent (b) is added to the ink composition in the form of a pigmentdispersion obtained by dispersing a pigment in a solvent using adispersant. Any known polymeric dispersant such as natural polymers andsynthetic polymers or surface active agent which has been conventionallyused for dispersing a pigment in a pigment-type ink can be favorablyused as the dispersant.

Natural polymers include for example proteins such as glue, gelatin,albumin and casein; natural rubbers such as gum arabic and tragacanthgum; glucosides such as saponin; alginic acid and derivatives thereofsuch as propylene glycol alginate, triethanol amine alginate andammonium alginate; and cellulose derivatives such as methyl cellulose,carboxymethyl cellulose, hydroxymethyl cellulose and ethyl hydroxymethylcellulose.

Synthetic polymers include for example polyvinyl alcohols; polyvinylpyrrolidones; acrylic resins such as polyacrylic acid, an acrylicacid-acrylonitrile copolymer, a potassium acrylate-acrylonitrilecopolymer, a vinyl acetate-acrylic acid ester copolymer and an acrylicacid-acrylic acid alkyl ester copolymer; styrene-acrylic resins such asa stylene-acrylic acid copolymer, a stylene-methacrylic acid copolymer,a stylene-methacrylic acid-acrylic acid alkyl ester copolymer, astylene-α-methylstylene-acrylic acid copolymer and astylene-α-methylstylene-acrylic acid-acrylic acid alkyl ester copolymer;a stylene-maleic acid copolymer; a stylene-maleic anhydride copolymer; avinylnaphthalene-acrylic acid copolymer; vinyl acetate resin such as avinyl acetate-ethylene copolymer, a vinyl acetate-fatty acid vinylethylene copolymer, a vinyl acetate-maleic acid ester copolymer, a vinylacetate-crotonic acid copolymer and a vinyl acetate-acrylic acidcopolymer; and salts of thereof. Polymers which comprises monomershaving a hydrophobic group and monomers having a hydrophilic group andpolymers which comprises monomers having both a hydrophobic group and ahydrophilic group are preferable. Preferred examples of the salts ofthese polymers include diethylamine, ammonia, ethylamine, triethylamine,propylamine, isopropylamine, dipropylamine, butylamine, isobutylamine,triethanolamine, diethanolamine, aminomethylpropanol and morpholine. Itis preferable that the weight average molecular weight of thesecopolymers be from 3,000 to 30,000, more preferably from 5,000 to15,000.

Surface active agents include for example anionic surface active agentssuch as salts of a fatty acid, higher alkylsulfates, salts of a higheralcohol sulfate ester, condensation products of a higher fatty acid andamino acid, sulfosuccinates, naphthnates, salts of a liquid fatty oilsulfate ester and alkyl allyl sulfate; cationic surface active agentssuch as salts of fatty amides, quaternary ammonium salts, sulfoniumsalts and phosphonium; and nonionic surface active agents such aspolyoxyethylene alkyl esters, polyoxyethylene alkyl esters, sorbitanalkyl esters and polyoxyethylene sorbitan alkyl esters.

The suitable amount of the dispersant is in the range of 0.06 to 3% byweight, preferably 0.125 to 3% by weight based the pigment.

Component (b)

Examples of the saccharides which can be used in the ink according tothe present invention include monosaccharides, disaccharides,oligosaccharides including trisaccharides and tetrasaccharides, andpolysaccharides. Preferred examples of the saccharicle include, glucose,mannose, fructose, ribose, xylose, arabinose, galactose, aldonic acid,glucitol (sorbitol), maltose, cellobiose, lactose, sucrose, trehaloseand maltotriose. The term "polysaccharides" herein means sugars in abroader sense, and includes those substances which are widelydistributed in the nature, such as alginic acid, α-cyclodextrin andcellulose.

Derivatives of the above saccharides include for example reducing sugarssuch as sugar-alcohols represented by the general formula of HOCH₂(CHOH)_(n) CH₂ OH in which n is an integer of 2 to 5, and deoxysugars;oxidized sugars such as aldonic acid and uronic acid; dehydrated sugarderivatives such as glycoseen; amino sugars; and thiosugars.

Sugar-alcohols are preferred, and specific examples thereof includemaltitol and sorbitol

The polyols having 5 or more hydroxyl groups which can be used arehydrocarbons which contain 5 or more, preferably 5 to 12 hydroxyl groupson a cyclic carbon chain. Preferable examples of such hydrocarbonsinclude inositol.

Component (c)

The resin emulsion which can be used is an emulsion consisting of wateras its continuous phase and the following resin component as itsdisperse phase. The resin component of the disperse phase include forexample acrylic resins, vinyl acetate resins, styrene-butadiene resins,vinyl chloride resins, acryl-styrene resins, polybutadiene resin andstylene resin.

According to the preferred embodiment of the present invention, it ispreferable that the resin be a polymer having both a hydrophilic moietyand a hydrophobic moiety. Although any particle diameter of the resincomponent is acceptable as long as an emulsion of the resin can beobtained, a preferable particle diameter is about 150 μm or less, morepreferably about 5 μm to 100 μm.

The resin emulsion can be prepared by mixing the resin particles and, ifnecessary, a surface active agent with water. For instance, an acrylicor styrene-acrylic resin emulsion can be obtained by mixing(meth)acrylate, or styrene and (meth)acrylate, and a surface activeagent with water, if necessary, together with (meth)acrylic acid. It ispreferable to make the mixing ratio of the resin component to thesurface active agent to approximately from 10:1 to 5:1. In the casewhere the amount of the surface active agent used is less than the aboverange, it is difficult to obtain an emulsion. On the other hand, whenthis amount is in excess of the above range, the resulting ink tends toundergo deterioration of water resistance and permeability. Although noparticular limitation is imposed on the surface active agent, preferableexamples thereof include: anionic surface active agents such as sodiumdodecylbenzenesulfonate, sodium laurate, ammonium salts ofpolyoxyethylene alkyl ether sulfate; and nonionic surface active agentssuch as polyoxyethylene alkyl ether, polyoxyethylene alkyl esterpolyoxyethylene sorbitan fatty acid ester, polyoxyethylene alkylphenylether, polyoxyethylene alkylamine polyoxyethylene alkylamide. Thesesurface active agents can be used either singly or as a mixture of twoor more.

The suitable proportion of the resin as a component of the dispersephase, and water is such that the amount of water is in the range of 60to 400 parts by weight, preferably in the range of 100 to 200 parts byweight per 100 parts by weight of the resin.

A conventionally known resin emulsion can be used as the resin emulsionin the present invention. Any one of the resin emulsions described in,for example, Japanese Laid-Open Patent Publication Nos. 1426/1987,56573/1991, 79678/1991, 160068/1991 and 18462/1992 can be used as it is.These publications are incorporated herein by reference.

A commercially available resin emulsion can also be used as the resinemulsion. Examples of such a resin emulsion include "Microgel E-1002"and "Microgel E-5002" (styrene-acrylic resin emulsions manufactured byNippon Paint Co., Ltd.), "SEE-9" (a styrene-acrylate resin emulsionmanufactured by Nippon Paint Co., Ltd.), "Boncoat 4001" (an acrylicresin emulsion manufactured by Dainippon Ink & Chemicals, Inc.),"Boncoat 5454" (a styrene-acrylic resin emulsion manufactured byDainippon Ink & Chemicals, Inc.), "AS-467A" (a styrene-acrylic resinemulsion manufactured by Daisel Chemical Industries Co., Ltd.), "SEA1014" (a styrene-acrylic resin emulsion manufactured by Nippon Zeon Co.,Ltd.), "Saibinol SK-200" (an acrylic resin emulsion manufactured bySaiden Chemical Industry Co., Ltd.).

According to the preferred embodiment of the present invention, a resinemulsion having a minimum film-forming temperature (MFT) of 50° C. orhigher is preferable.

Ink Composition

The ink composition according to the present invention comprisespreferably 0.1% to 40% by weight, more preferably 0.5% to 30% by weightof the component (b). When the amount of the component (b) is less thanthe above range, the effects of the component (b) cannot be obtained. Onthe other hand, when this amount is in excess of the above range, thecomponent (b) cannot be easily dissolved in water.

The ink composition of the present invention comprises preferably 0.1%to 40% by weight, more preferably 1% to 25% by weight of the resinemulsion. When the amount of the resin emulsion is less than the aboverange, the effects of the resin emulsion cannot be expected. On theother hand, when this amount is in excess of the above range, theresulting ink composition cannot produce an image with a high opticaldensity, and tends to have an excessively high viscosity.

The amount of the pigment in the ink composition is preferably about0.5% to 25% by weight, more preferably about 2% to 15% by weight.

The ink composition according to the present invention forms anextremely thin and brittle film at a nozzle tip. This film preventsevaporation of water and organic solvent from the ink composition, sothat the solid components are not separated out. The ink composition isthus prevented from causing obstruction in a nozzle. On the other hand,this film is so thin and brittle that it can be readily broken by ausual cleaning operation (reset operation). It is therefore possible toinitiate printing right after this operation. The ink composition of thepresent invention can produce a high-density image having highmoisture-abrasion resistance. Without intending to be bound by theory,it is believed that the apparent diameter of the pigment particles isincreased by adsorption of the resin emulsion and the component (b), sothat the pigment cannot easily permeate the fibers of paper. Thus, thepermeability of the ink is moderated, and the pigment particles arefully sustained on the fibers of paper. What is more interesting is thatthe ink composition of the present invention is excellent inpreservability. It can be considered that the dispersion stability ofthe pigment particles is enhanced by the adsorption of the resinemulsion and the component (b) to the pigment particles.

According to the preferred embodiment of the present invention, theweight ratio of the resin emulsion: the component (b) in the inkcomposition of the invention is preferably 1:0.5 or more but less than1:50, more preferably in the range of 1:0.5 to 1:40. The above-describedadvantageous properties of the ink composition according to the presentinvention can be enhanced by employing this weight ratio and adding theresin emulsion having a minumum film-forming temperature of 50° C. orhigher in combination.

According to the preferred embodiment of the present invention, the inkcomprises the pigment, the component (b), and the resin emulsion in thefollowing proportion: the weight ratio of the pigment: the resincomponent of the resin emulsion is preferably in the range of 1:0.1 to1:2, more preferably in the range of 1:0.1 to 1:1.5, and the weightratio of the component (b): the total amount of the pigment and theresin component of the resin emulsion is preferably in the range of1:0.1 to 1:2, more preferably in the range of 1:0.18 to 1:2.

According to the preferred embodiment of the present invention, it ispreferable that the ink composition of the present invention furthercomprise a wetting agent.

The wetting agents include for example diethylene glycol, polyethyleneglycol, polypropylene glycol, ethylene glycol, propylene glycol,butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thioglycol,hexylene glycol, glycerine, trimethylolethane, trimethylolpropane, urea,2-pyrrolidone, N-methyl-2-pyrrolidone and1,3-dimethyl-2-imidazolidinone. The wetting agents having an ethyleneoxide group are particularly preferred, and diethylene glycol is mostpreferred. In addition to the wetting agent, it is preferable to furtheradd an organic solvent having a low boiling point. Preferred examples ofsuch an organic solvent include methanol, ethanol, n-propanol,iso-propanol, n-butanol, sec-butanol, tert-butanol, iso-butanol,n-pentanol, ethylene glycol monomethyl ether, ethylene glycol monoethylether, diethylene glycol monomethyl ether, diethylene glycol monoethylether, triethylene glycol monomethyl ether and triethylene glycolmonoethyl ether. Monovalent alcohols are particularly preferred.

The amount of the wetting agent is preferably in the range of 0.5% to40% by weight, more preferably 2% to 20% by weight of the inkcomposition. The amount of the organic solvent having a low boilingpoint is preferably in the range of 0.5% to 10% by weight, morepreferably 1.5% to 6% by weight of the ink composition.

According to the preferred embodiment of the present invention, it ispreferable that the weight ratio of the total amount of the pigment andthe resin component of the resin emulsion: the dispersant be from 1:0.02to 1:0.5, and the weight ratio of the dispersant: the component (b) befrom 1:0.5 to 1:50.

It can be considered that the resin emulsion also acts as a dispersant.It is therefore possible to further add the resin emulsion instead ofadding the dispersant.

The ink composition can contain an optional additives in order toimprove the properties of the ink composition. Specific examples of suchadditives include a viscosity modifier, a surface tension modifier, a pHadjustor, an antifungal agent and a preservative.

The ink composition according to the present invention can be preparedby dispersing and mixing the above-described components by a propermethod. A preferable manner is such that the components except anorganic solvent and a volatile component are mixed in a properdispersion mixer such as a ball mill, a sand mill, an atrittor, a rollmill, an agitator mill, a Henschel mixer, a colloid mill, an ultrasonichomogenizer, a jet mill, an angmill, to obtain a homogeneouscomposition, and an organic solvent and a volatile component are thenadded to this composition. It is preferable to subject the mixture thusobtained to filtration, preferably filtration using a metal filter, amembrane filter or the like under reduced pressure or under pressure, orcentrifugal separation in order to remove large particles and foreignmatters which tend to be a cause of obstruction in a nozzle.

The present invention will now be explained more specifically byreferring to the following Examples, which should not be construed aslimiting the present invention.

In the following examples, "MFT" denotes a minimum film-formingtemperature, and percentages are by weight.

EXAMPLE 1

    ______________________________________                                        Carbon black MA7         2%                                                   (manufactured by Mitsubishi                                                   Chemical Industries, Ltd.)                                                    Styrene-maleic anhydride copolymer                                                                     4%                                                   (dispersant)                                                                  Microgel E-1002          25%                                                  (Styrene-acrylic resin emulsion,                                              resin content: 19.9%, MFT = about 80° C.,                              manufactured by Nippon Paint Co., Ltd.)                                       α-Cyclodextrin     14%                                                  Diethylene glycol        5%                                                   Ethanol                  5%                                                   Pure water               45%                                                  ______________________________________                                    

The above components except diethylene glycol and ethanol were mixed,and the mixture was dispersed in a sand mill (manufactured by YasukawaSeisaku-sho K.K.) along with glass beads (diameter: 1.7 mm, 1.5 times(w/w) the quantity of the mixture) for two hours. Thereafter, the glassbeads were removed, and diethylene glycol and ethanol were added to themixture. The resulting mixture was stirred at room temperature for 20minutes, and then filtered through a 5-μm membrane filter, whereby anink for ink jet printing was obtained.

EXAMPLE 2

    ______________________________________                                        Carbon black MA100    3%                                                      (manufactured by Mitsubishi                                                   Chemical Industries, Ltd.)                                                    Polyvinyl alcohol     0.5%                                                    (dispersant)                                                                  Boncoat 4001          2%                                                      (acrylic resin emulsion,                                                      resin content: 50%, MFT = 5° C.,                                       manufactured by Dainippon                                                     Ink & Chemicals, Inc.)                                                        Sucrose               15%                                                     Glycerine             10%                                                     n-Propanol            2%                                                      Pure water            67.2%                                                   ______________________________________                                    

The above components except glycerine and n-propanol were mixed, and themixture was dispersed in a sand mill (manufactured by YasukawaSeisaku-sho K. K.) along with zirconium beads (diameter: 1.2 mm, 0.8times (w/w) the quantity of the mixture) for two hours. Thereafter, thebeads were removed, and glycerine and n-propanol were added to themixture. The resulting mixture was stirred at room temperature for 20minutes, and then filtered through a 5-μm membrane filter, whereby anink for ink jet printing was obtained.

EXAMPLE 3

    ______________________________________                                        Carbon black #40        2.5%                                                  (manufactured by Mitsubishi                                                   Chemical Industries, Ltd.)                                                    Styrene-acrylic acid copolymer                                                                        2%                                                    (dispersant)                                                                  Microgel E-5002         0.85%                                                 (Styrene-acrylic resin emulsion,                                              resin content: 29.2%, MFT = 80° C.,                                    manufactured by Nippon Paint Co., Ltd.)                                       Inositol                10%                                                   2-Pyrrolidone           4%                                                    Ethanol                 5%                                                    Pure water              75.65%                                                ______________________________________                                    

The above components except 2-pyrrolidone and ethanol were mixed, andthe mixture was dispersed in a sand mill (manufactured by YasukawaSeisaku-sho K. K.) along with glass beads (diameter: 1.0 mm, 1.2 times(w/w) the quantity of the mixture) for two hours. Thereafter, the glassbeads were removed, and 2-pyrrolidone and ethanol were added to themixture. The resulting mixture was stirred at room temperature for 20minutes, and then filtered through a 5-μm membrane filter, whereby anink for ink jet printing was obtained.

EXAMPLE 4

    ______________________________________                                        C.I. Pigment black 1  5%                                                      Polyvinylpyrrolidone  1%                                                      (dispersant)                                                                  Boncoat 5454          15%                                                     (styrene-acrylic resin emulsion,                                              resin content: 45%, MFT = 4° C.,                                       manufactured by Dainippon Ink &                                               Chemical, Inc.)                                                               Xylose                6%                                                      Glycerine             10%                                                     n-Propanol            4%                                                      Pure water            59%                                                     ______________________________________                                    

The above components except glycerine and n-propanol were mixed, and theresulting mixture was dispersed in a sand mill (manufactured by YasukawaSeisaku-sho K.K.) along with glass beads (diameter: 1.7 mm, 1.5 times(w/w) the quantity of the mixture) for two hours. Thereafter, the glassbeads were removed, and glycerine and n-propanol were added to themixture. The resulting mixture was stirred at room temperature for 20minutes, and then filtered through a 5-μm membrane filter, whereby anink for ink jet printing was obtained.

EXAMPLE 5

    ______________________________________                                        Carbon black MA7     2%                                                       Styrene-acrylic acid copolymer                                                                     0.8%                                                     (dispersant)                                                                  Microgel E-1002      3%                                                       Sucrose              5.6%                                                     Diethylene glycol    5%                                                       Ethanol              5%                                                       Pure water           78.6%                                                    ______________________________________                                    

The above components except diethylene glycol and ethanol were mixed,and the mixture was dispersed in a sand mill (manufactured by YasukawaSeisaku-sho K.K.) along with glass beads (diameter: 1.7 mm, 1.5 times(w/w) the quantity of the mixture) for two hours. Thereafter, the glassbeads were removed, and diethylene glycol and ethanol were added to themixture. The resulting mixture was stirred at room temperature for 20minutes, and then filtered through a 5-μm membrane filter, whereby anink for ink jet printing was obtained.

EXAMPLE 6

    ______________________________________                                        Carbon black MA100      3%                                                    Polyvinyl alcohol       0.5%                                                  (dispersant)                                                                  SAE 1014                                                                      (Styrene-acrylic resin emulsion,                                              resin content: 40%, MFT = 70-90° C.                                    manufactured by Nippon Zeon Co., Ltd.)                                        Sorbitol                5%                                                    Glycerine               10%                                                   n-Propanol              2%                                                    Pure water              69.5%                                                 ______________________________________                                    

The above components except glycerine and n-propanol were mixed, and themixture was dispersed in a sand mill (manufactured by YasukawaSeisaku-sho K. K.) along with glass beads (diameter: 1.2 mm, 0.8 times(w/w) the quantity of the mixture) for two hours. Thereafter, the glassbeads were removed, and glycerine and n-propanol were added to themixture. The resulting mixture was stirred at room temperature for 20minutes, and the filtered through a 5-μm membrane filter, whereby an inkfor ink jet printing was obtained.

EXAMPLE 7

    ______________________________________                                        Carbon black Raven 1080                                                                              2.4%                                                   (available from Columbian                                                     Carbon Japan Limited)                                                         Styrene-maleic anhydride copolymer                                                                   0.5%                                                   (dispersant)                                                                  Saibinol SK-200        0.88%                                                  (acrylic resin emulsion,                                                      resin content: 49.5%, MFT >80° C.,                                     manufactured by Saiden Chemical                                               Industry Co., Ltd.)                                                           Maltotriose            15%                                                    Urea                   4%                                                     Ethanol                5%                                                     Pure water             72.22%                                                 ______________________________________                                    

The above components except urea and ethanol were mixed, and the mixturewas dispersed in a sand mill (manufactured by Yasukawa Seisaku-sho K.K.) along with glass beads (diameter: 1.0 mm, 1.2 times (w/w) thequantity of the mixture) for two hours. Thereafter, the glass beads wereremoved, and urea and ethanol were added to the mixture. The resultingmixture was stirred at room temperature for 20 minutes, and thenfiltered through a 5-μm membrane filter, whereby an ink for ink jetprinting was obtained.

EXAMPLE 8

    ______________________________________                                        C.I. Pigment black 1  8%                                                      Polyvinylpyrrolidone (dispersant)                                                                   1%                                                      Boncoat 5454          5%                                                      Maltitol              10%                                                     1,5-Pentanediol       10%                                                     n-Propanol            4%                                                      Pure water            62%                                                     ______________________________________                                    

The above components except 1,5-pentanediol and n-propanol were mixed,and the mixture was dispersed in a sand mill (manufactured by YasukawaSeisaku-sho K.K.) along with glass beads (diameter: 1.7 mm, 1.5 times(w/w) the quantity of the mixture) for two hours. Thereafter, the glassbeads were removed, and 1,5-pentanediol and n-propanol were added to themixture. The resulting mixture was stirred at room temperature for 20minutes, and then filtered through a 5-μm membrane filter, whereby anink for ink jet printing was obtained.

EXAMPLE 9

    ______________________________________                                        Carbon black MA100    5%                                                      Potassium acrylate-acrylonitrile                                                                    1%                                                      copolymer (dispersant)                                                        Microgel E-1002       4%                                                      Sucrose               8%                                                      Glycerine             8%                                                      Ethanol               6%                                                      Pure water            68%                                                     ______________________________________                                    

The above components were mixed by a jet mill. It was confirmed bymicroscopic observation that the particle diameters were within therange of 1 μm or less. The mixture was filtered through a 3-μm membranefilter under pressure, whereby an ink for ink jet printing was obtained.

In the following Examples 10 to 13, inks for ink jet printing wererespectively prepared in the same manner as in Example 9.

EXAMPLE 10

    ______________________________________                                        Carbon black MA100   4%                                                       Styrene-acrylic acid copolymer                                                                     1.2%                                                     (dispersant)                                                                  Microgel E-1002      8%                                                       α-Cyclodextrin 3%                                                       Diethylene glycol    12%                                                      2-Propanol           3%                                                       Pure water           68.8%                                                    ______________________________________                                    

EXAMPLE 11

    ______________________________________                                        Carbon black MA7      2%                                                      Styrene-maleic acid copolymer                                                                       0.5%                                                    (dispersant)                                                                  SG-60                 1.2%                                                    (Styrene-acrylic resin emulsion,                                              resin content: 41%, MFT = 92° C.,                                      manufactured by Gifu Shellac                                                  Mfg. Co., Ltd.)                                                               Sucrose               10%                                                     Urea                  2%                                                      2-Propanol            5%                                                      Pure water            79.3%                                                   ______________________________________                                    

EXAMPLE 12

    ______________________________________                                        Carbon black MA7       2%                                                     Styrene-maleic acid copolymer                                                                        5%                                                     (dispersant)                                                                  Polyvinylpyrrolidone   1%                                                     (dispersant, average molecular                                                weight: about 40,000, manufactured                                            by Tokyo Kasei Kogyo Co., Ltd.)                                               SEE-9                  7.5%                                                   (Styrene-acrylate resin emulsion                                              resin content: 40%, MFT =                                                     50-80° C., manufactured by                                             Nippon Paint Co., Ltd.)                                                       Xylose                 1.5%                                                   Polyethylene glycol    8%                                                     Ethanol                4%                                                     Pure water             71%                                                    ______________________________________                                    

EXAMPLE 13

    ______________________________________                                        Pigment KET Red 309   3%                                                      (manufactured by Dainippon Ink                                                & Chemicals, Inc.                                                             Potassium acrylate-acrylonitrile                                                                    0.5%                                                    copolymer (dispersant)'                                                       Denka Poval           1%                                                      (dispersant, manufactured by                                                  by Denki Kagaku Kogyo K.K.)                                                   AS-467A               4.3%                                                    (Stylene-acrylic acid resin                                                   emulsion, resin content: 46%,                                                 MFT = 70-90° C., manufactured                                          by Daisel Chemical Industries                                                 Co., Ltd.)                                                                    Inositol              10%                                                     Diethylene glycol     5%                                                      1-Propanol            5%                                                      Pure water            71.2%                                                   ______________________________________                                    

EXAMPLE 14

    ______________________________________                                        Carbon black MA100    2%                                                      Salt of acrylic acid-                                                         acrylonitrile copolymer (dispersant)                                                                0.2%                                                    Microgel E-1002       2.5%                                                    Maltose               1.2%                                                    Diethylene glycol     5%                                                      Ehtanol               3%                                                      Pure water            86.1%                                                   ______________________________________                                    

The above components were mixed by a jet mill. It was confirmed bymicroscopic observation that the particle diameters were within therange of 1 μm or less. The mixture was filtered through a 3-μm membranefilter under pressure, whereby an ink for ink jet printing was obtained.

In the following Examples 15 to 21, inks for ink jet printing wererespectively prepared in the same manner as in Example 14.

EXAMPLE 15

    ______________________________________                                        Carbon black MCF-88   5%                                                      (manufactured by Mitsubishi                                                   Chemical Industries, Ltd.)                                                    Salt of acrylic acid- 2.2%                                                    acrylonitrile copolymer (dispersant)                                          SEE-9                 0.75%                                                   Inositol              3%                                                      Ethylene glycol       5%                                                      I-Propanol            1%                                                      Urea                  1%                                                      Pure water            82.05%                                                  ______________________________________                                    

EXAMPLE 16

    ______________________________________                                        Carbon black MA7      4%                                                      Polyvinylpyrrolidone  0.8%                                                    (dispersant, average molecular                                                weight: about 40,000, manufactured                                            by Tokyo Kasei Kogyo Co., Ltd.)                                               Microgel E-1002       15.1%                                                   Sucrose               4%                                                      Urea                  2.2%                                                    2-Propanol            2%                                                      Pure water            71.9%                                                   ______________________________________                                    

EXAMPLE 17

    ______________________________________                                        Carbon black Raven 150                                                                            3%                                                        (available from Columbian                                                     Carbon Japan Limited)                                                         Salt of styrene-acrylic acid                                                                      0.18%                                                     copolymer (dispersant)                                                        SG-60               7.3%                                                      Sorbitol            2%                                                        Urea                3%                                                        Glycerine           5%                                                        1-Butanol           0.5%                                                      Pure water          79.02%                                                    ______________________________________                                    

EXAMPLE 18

    ______________________________________                                        Pigment KET BLUE EX-1 5%                                                      (manufactured by Dainippon Ink                                                & Chemicals Inc.)                                                             Salt of styrene-acrylic acid                                                                        1%                                                      copolymer (dispersant)                                                        Microgel E-1002       1.5%                                                    Galactose             2%                                                      Sucrose               7.5%                                                    Diethylene glycol     5%                                                      Ethanol               4%                                                      Pure Water            74%                                                     ______________________________________                                    

EXAMPLE 19

    ______________________________________                                        Pigment KET YELLOW 403                                                                              3%                                                      (manufactured by Dainippon Ink                                                & Chemicals, Inc.)                                                            Salt of styrene-acrylic acid                                                                        0.4%                                                    copolymer (dispersant)                                                        SAE 1014              5%                                                      Maltitol              0.5%                                                    Alginic acid          0.5%                                                    Urea                  2%                                                      Diethylene glycol     5%                                                      Ethanol               2%                                                      Pure Water            81.6%                                                   ______________________________________                                    

EXAMPLE 20

    ______________________________________                                        Carbon black MA7    4%                                                        Salt of styrene-acrylic acid                                                                      0.8%                                                      copolymer (dispersant)                                                        Saibinol SK-200     1.2%                                                      Glucose             12%                                                       Thiourea            2%                                                        Ethanol             3%                                                        Pure water          77%                                                       ______________________________________                                    

EXAMPLE 21

    ______________________________________                                        Carbon black MA7    4%                                                        Salt of styrene-acrylic acid                                                                      0.8%                                                      copolymer (dispersant)                                                        Microgel E1002      3%                                                        SAE1014             1.3%                                                      Maltitol            4.2%                                                      Urea                3%                                                        Diethylene glycol   5%                                                        Ethanol             1.5%                                                      Pure water          77.2%                                                     ______________________________________                                    

COMPARATIVE EXAMPLE 1

    ______________________________________                                        Carbon black MA100 10%                                                        Gelatin (dispersant)                                                                              4%                                                        Inositol            7%                                                        Ethylene glycol    15%                                                        Ethanolamine        1%                                                        Pure water         60%                                                        ______________________________________                                    

The above components were mixed, and the mixture was dispersed in a sandmill (manufactured by Yasukawa Seisaku-sho K. K.) along with glass beads(diameter: 1.0 mm, 1.2 times (w/w) the quantity of the mixture) for twohours. The resulting mixture was then filtered through a 5-μm membranefilter, whereby an ink for ink jet printing was obtained.

The following Comparative Examples 2 and 3 were respectively prepared inthe same manner as in Comparative Example 1.

COMPARATIVE EXAMPLE 2

    ______________________________________                                        C.I. Pigment black 1  8%                                                      Lunox 1500A           3.4%                                                    (anionic surface active agent                                                 manufactured by Toho Chemical                                                 Industry Co., Ltd.)                                                           Lunal 310             1%                                                      (anionic surface active agent                                                 manufactured by Toho Chemical                                                 Industry Co., Ltd.)                                                           Primal AC-61          18%                                                     (acrylic resin emulsion,                                                      resin content: 46%, MFT = 17° C.,                                      manufactured by Japan Acrylic                                                 Chemical Co., Ltd.)                                                           Ethylene glycol       7%                                                      Pure water            62.6%                                                   ______________________________________                                    

COMPARATIVE EXAMPLE 3

    ______________________________________                                        Carbon black MA7      3%                                                      Salt of styrene-maleic anhydride                                                                    0.1%                                                    copolymer (dispersant)                                                        Microgel E1002        15%                                                     Polyethylene glycol   4.5%                                                    Urea                  7%                                                      1-Propanol            3%                                                      Pure water            67.4%                                                   ______________________________________                                    

Evaluation Test

The properties of the above ink compositions were evaluated in thefollowing manner:

(a) Obstruction

The ink composition was placed in an ink jet printer HG-5130(manufactured by Seiko Epson Corporation). After an image wascontinuously printed by the printer for 10 minutes, the printing wasdiscontinued. The printer was then allowed to stand without covering itshead with a cap in an environment of 40° C. and 25% RH for two weekswhen the ink was one of those obtained in Examples 1-8 and ComparativeExamples 1 and 2, and at room temperature for 1 day when the ink was oneof those obtained in Examples 9-21 and Comparative Examples 3. After thenozzle was subjected to a cleaning operation, printing was initiated.The obstruction property of the ink was evaluated by the number of timesof the cleaning operation necessary to obtain an image equal to theinitially obtained one, which was free from defects such as tailings andvoids.

The results are as shown in the tables below. In the tables,

A: an image equal to the initially obtained one was obtained after thecleaning operation was repeated 0 to 5 times;

B: an image equal to the initially obtained one was obtained after thecleaning operation was repeated 6 to 10 times; and

C: an image equal to the initially obtained one was obtained even afterthe cleaning operation was repeated 11 times or more.

(b) Preservability

A laboran screw tube bottle was filled with 50 cc of the ink, andallowed to stand at a temperature of 50° C. when the ink was one ofthose obtained in Examples 1-8 and Comparative Examples 1 and 2, and attemperatures of both -20° C. and 50° C. when the ink was one of thoseobtained in Examples 9-21 and Comparative Examples 3. After two months,the presence of precipitate in the ink was observed.

The results are as shown in the tables below. In the tables, regardingthe inks of Examples 1-8 and Comparative Examples 1 and 2

A: no precipitate was found, and

C: precipitate was found, and regarding the inks of Examples 9-21 andComparative Examples 3

A: no precipitate was found in both of the inks preserved at -20° C. and50° C.,

B: precipitate was found only in the ink preserved at -20° C., and

C: precipitate was found in both of the inks preserved at -20° C. and50° C.

(c) Water Resistance

An image was printed on a sheet of "Xerox P Pager" (Trademark,manufactured by Xerox Corp.) by an ink jet printer HG-5130. This out putsample was air-dried for 24 hours, and then immersed in 100 cc of water.The change in the optical density of the printed image before and afterthe immersion was determined by a Macbeth PCM II (manufactured byMacbeth Corp.).

The results are as shown in the tables below. In the tables,

A: the change in the OD value before and after the immersion was 0.5 orless,

B: the change in the OD value before and after the immersion was from0.5 to 1.0, and

B: the change in the OD value before and after the immersion was 1.0 ormore.

(d) Resistance to Finger Abrasion

An image was printed on a sheet of "Xerox P Paper" (Trademark,manufactured by Xerox Corp.) by an ink jet printer HG-5130. After beingair-dried for 24 hours, the out put sample was rubbed by fingers in anenvironment of 25° C. and 50% RH, and visually observed whether theimage was smudged or not.

The results are as shown in the tables below. In the tables,

A: no smudge was observed in the printed image,

B: smudge was slightly observed in the printed image, but the characterswere able to be read, and

C: the printed image was so smudged that the characters were not able tobe read.

(e) Light Resistance

An image was printed on a sheet of "Xerox P pager" (Trademark,manufactured by Xerox Corp.) by an ink jet printer HG-5130, and this output sample was air-dried for 24 hours. Light was then irradiated to thesample by a xenon fade tester XF-15N (manufactured by Shimadzu Corp.) at70% RH for 50 hours. The change in the L*a*b color difference before andafter the irradiation was determined by a differential colorimeterCR-121 (manufactured by Minolta Co., Ltd.).

The results are as shown in the tables below. In the tables,

A: ΔE≦10, and

C: ΔE>10

(f) Image Quantity (Blur)

An image was printed by an ink jet printer HG-5130 on each one of thefollowing papers: "Xerox P Paper" (Trademark, manufactured by XeroxCorp.), "Ricopy 6000 Paper" (Trademark, manufactured by Ricoh Co.,Ltd.), "Xerox 4024 Paper" (Trademark, manufactured by Xerox Corp.), and"Neenah Bond Paper" (Trademark, manufactured by Kimberly-ClarkCorporation). The image was visually observed whether it was blurred ornot.

The results are as shown in the tables below. In the tables.

A: the printed image was sharp and free from blur,

B: the printed image was blurred like whiskers, and

C: the printed image was so blurred that the characters had fuzzyoutlines.

(g) Image Quality (Optical Density)

The reflection optical density of the printed image obtained in theabove item "Image Quality (Blur)" was measured by a Macbeth OCMII.

The results are as shown in the tables below.

(h) Rapid Drying Properties

100% Duty printing was conducted by an ink jet printer HG-5130 on fourtypes of papers which were the same as those used in the above item"Image Quality (Blur)". The rapid drying properties of the ink wereevaluated by the time required to dry up the printed image to such adegree that a hand was not stained with the ink upon touching theprinted image.

The results are as shown in the tables below. In the tables,

A: the time was within 30 seconds, and

C: the time was more than 30 seconds.

(i) Unevenness of Printing

100% Duty printing was conducted on "Ricopy 6000 paper" (Trademark,manufactured by Ricoh Co., Ltd.) and "Canon Dry Paper" (Trademark,manufactured by Canon Inc.) by an ink jet printer HG-5130. The OD valuesof any five points on the printed image were measured with MacbethPCMII, and then the average of the five values is obtained. Thisprocedure was repeated five times to give five average values. Thedifference between the maximum average value and minimum average valuewas obtained.

The results are as shown in the tables below. In the tables,

A: the difference was 0.4 or less, i.e., unevenness was not virtuallyfound in the printed image,

B: the difference was 0.4 to 0.5, i.e. unevenness raised no practicalproblem, and

C: the difference was more than 0.5, i.e. unevenness made the image nopractical value.

                                      TABLE                                       __________________________________________________________________________                  Example                                                                       1  2  3   4  5   6  7   8  9   10  11 11  13 14                 __________________________________________________________________________    Resin component of resin                                                                    2.8                                                                              15 40.3                                                                              0.89                                                                             9.4 2.5                                                                              34.4                                                                              4.44                                                                             10  1.875                                                                             20 0.5 5  2.4                emulsion: Component (b)                                                       Pigment: Resin component                                                                    2.5                                                                              0.33                                                                             0.1 1.35                                                                             0.3 0.67                                                                             0.18                                                                              0.28                                                                             0.16                                                                              0.4 0.25                                                                             1.5 0.67                                                                             0.25               of resin emulsion1                                                            Component (b): Pigment +                                                                    0.5                                                                              0.27                                                                             0.275                                                                             1.96                                                                             0.463                                                                             1  0.189                                                                             1.03                                                                             0.725                                                                             1.87                                                                              0.25                                                                             3.33                                                                              0.5                                                                              2.08               Resin component of resin                                                      emulsion                                                                      (a) Obstruction                                                                             A  A  A   A  A   A  A   A  A   A   A  A   A  A                  (b) Preservability                                                                          A  A  A   A  A   A  A   A  A   A   A  A   A  A                  (c) Water resistance                                                                        A  A  A   A  A   A  A   A  A   A   A  A   A  A                  (d) Finger-abrasion                                                                         A  A  A   A  A   A  A   A  A   A   A  A   A  A                     resistance                                                                 (e) Light resistance                                                                        A  A  A   A  A   A  A   A  A   A   A  A   A  A                  (f) Blur      A  A  A   A  A   A  A   A  A   A   A  A   A  A                  (g) Optical density                                                                         1.32                                                                             1.37                                                                             1.35                                                                              1.40                                                                             1.41                                                                              1.44                                                                             1.43                                                                              1.46                                                                             --  --  -- --  -- 1.40               (h) Rapid drying property                                                                   A  A  A   A                A   A   A  A   A  A                  (i) Unevenness                                                                              B  B  B   B  A   A  A   A  A   A   A  B   B  A                  __________________________________________________________________________                                   Example              Comparative Example                                      15 16 17 18 19 20 21 1   2  3                  __________________________________________________________________________                     Resin component of resin                                                                    10 1.33                                                                             0.67                                                                             31.7                                                                             0.5                                                                              20 3.82                                                                             --*.sup.1                                                                         --*.sup.2                                                                        --*.sup.2                           emulsion: Component (b)                                                       Pigment: Resin component                                                                    0.06                                                                             0.75                                                                             1  0.06                                                                             0.67                                                                             0.15                                                                             0.28                                                                             --*.sup.1                                                                         1.04                                                                             1                                   of resin emulsion1                                                            Component (b): Pigment +                                                                    1.77                                                                             1.75                                                                             3.00                                                                             0.56                                                                             5.06                                                                             0.38                                                                             1.21                                                                             0.7 --*.sup.2                                                                        --*.sup.2                           Resin component of resin                                                      emulsion                                                                      (a) Obstruction                                                                             A  A  A  A  A  A  A  A   C  C                                   (b) Preservability                                                                          A  A  A  A  A  A  A  A   A  C                                   (c) Water resistance                                                                        A  A  A  A  -- -- -- C   A  --                                  (d) Finger-abrasion                                                                         A  A  A  A  -- -- -- C   A  --                                     resistance                                                                 (e) Light resistance                                                                        A  A  A  A  -- -- -- A   A  --                                  (f) Blur      A  A  A  A  A  A  A  B   B  B                                   (g) Optical density                                                                         1.59                                                                             1.44                                                                             1.41                                                                             1.59                                                                             1.42                                                                             1.45                                                                             1.42                                                                             1.17                                                                              1.31                                                                             1.26                                (h) Rapid drying property                                                                   A  A  A  A  -- -- -- C   C  --                                  (i) Unevenness                                                                              A  A  B  B  B  A  A  C   C  C                  __________________________________________________________________________     *.sup.1 the resin emulsion was not contained, and                             *.sup.2 the component (b) was not contained.                             

What is claimed is:
 1. An aqueous ink composition for ink jet printingcomprising:(a) a pigment, (b) a component selected from the groupconsisting of saccharides, derivatives thereof and polyols having 5 ormore hydroxyl groups, and (c) a resin emulsion.
 2. An ink compositionaccording to claim 1, wherein the saccharides as the component (b) areselected from the group consisting of monosaccharides, disaccharides,oligosaccharides and polysaccharides.
 3. An ink composition according toclaim 1, wherein the derivatives of the saccharides as the component (b)are reducing sugars, oxidized sugars, dehydrated sugar derivatives,amino sugars or thiosugars of the saccharides.
 4. An ink compositionaccording to claim 1, wherein the polyol as the component (b) isinositol.
 5. An ink composition according to claim 1, wherein the resinemulsion has a minimum film-forming temperature of 50° C. or more.
 6. Anink composition according to claim 1, wherein the resin emulsion isselected from the group consisting of acrylic resin emulsions, vinylacetate resin emulsion, vinyl chloride resin emulsions, acryl-styreneresin emulsions polybutadiene resin emulsions and stylene resinemulsions.
 7. An ink composition according to claim 1, wherein theweight ratio of a resin component of the resin emulsion: the component(b) is from 1:0.5 or more but less than 1:50.
 8. An ink compositionaccording to claim 1, wherein the weight ratio of the pigment: a resincomponent of the resin emulsion is from 1:0.1 to 1:2, and the weightratio of the component (b): the total amount of the pigment and theresin component of the resin emulsion is from 1:0.1 to 1:2.
 9. An inkcomposition according to claim 1, wherein a resin component of the resinemulsion is present in an amount of from 0.1 to 40% by weight based onthe ink composition.
 10. An ink composition according to claim 1,wherein the component (b) is present in an amount of from 0.1 to 40% byweight based on the ink composition.
 11. An ink composition according toclaim 1, further comprising a wetting agent.
 12. An ink compositionaccording to claim 11, further comprising an organic solvent having alow boiling point.
 13. An ink composition according to claim 1, whereinthe component (a) is a pigment dispersion obtained by dispersing apigment in a solvent using a dispersant.
 14. An ink compositionaccording to claim 13, wherein the weight ratio of the total amount ofthe pigment and the resin component of the resin emulsion: thedispersant is from 1:0.02 to 1:0.5, and the weight ratio of thedispersant: the component (b) is from 1:0.5 to 1:50.
 15. An inkcomposition according to claim 13, wherein the pigment dispersionfurther comprises an amine.